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July 8, 2010
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Since the release of the 2010 Yamaha YZ450F the aftermarket has been pushing hard to catch up. Not Pro Circuit. They were on the ball when it came to building a full-race 2010 YZ450F. Many motocross fans associate Pro Circuit with Kawasaki because of their winning motocross race team, but don’t think of Pro Circuit as a one-trick pony. Before they were a Kawasaki team, they ran Team Honda’s 125 team. This is the shop that made every Suzuki engine that Ricky Carmichael raced, made Glenn Kearney’s GNCC Husqvarna engine, and built the engines for everyone from Canidae Suzuki to Geico Honda. To say that Pro Circuit has the field covered is an understatement.

What was different about our Pro?Circuit YZ450F engine internals? Nothing, the MXA wrecking crew tried to be sensible for once?so we didn’t modify every part of the YZ450F. We left the piston, cams and valves alone.

Pro Circuit had spent well over 100 hours riding, testing, researching and dynoing their 2010 Yamaha YZ450F mods. The tireless dedication that Pro Circuit poured into the bike was for good reason. Finding the chinks in the YZ450F’s armor and addressing those issues would be great news for consumers, and would prove prosperous in sales numbers.

But Pro Circuit isn’t driven by money. Oh, don’t get us wrong, Mitch Payton needs to pay the electric bill on his massive Corona, California, shop, but his compulsive fascination with improving motocross bikes means that when he gets to the point where other hop-up companies might think the bike is good enough, Mitch keeps on pushing. What really makes many Pro Circuit products stand out is how they offer a performance advantage while being aesthetically pleasing. Call it bling with a bang.

The MXA wrecking crew was anxious to get our hands on Pro Circuit’s 2010 YZ450F technology?so we asked them to build a purpose-built test bike for us. With a deadpan face Mitch Payton replied, “I thought you would never ask.”


We should clear up any misgivings of YZ450F owners on a budget. Given MXA‘s unlimited supply of money, we tend to splurge when we have project bikes built. We don’t want to leave any stone unturned?so we often go whole hog. We are not averse to spending $6750 on a Showa A-Kit suspension, $3000 on full-blown race engines, $4530 for titanium bolt kits or $1440 on Excel A-60 rims laced to Talon magnesium hubs. However, this time we skipped most of the high-dollar items. Why? Although the 2010 YZ450F might well benefit from those modifications, we wanted to focus on the meat-and-potatoes of the bike?suspension, exhaust, linkage and gearing. Don’t get us wrong, we still spent a lot of money. But, it is up to you to pick and choose the parts you feel you need and can afford.

The most expensive single part on our Pro Circuit YZ450F was the Ti-4R full-titanium race exhaust system ($999.95). As for the single area that got the most attention, the suspension was the hands-down winner. We spent $1252.40 (not including the price of the bladder cap kit) on the YZ450F’s Kayaba SSS suspension. Pro Circuit’s suspension guru, Bones Bacon, revalved the forks and shock, replaced the springs, put in a bladder cap and anodized kit, as well as special spring tubes. To top it off, Bones installed a 1-1/2mm longer rising-rate shock linkage ($224.95).

Other Pro Circuit-specific products were axle blocks, a radiator hose kit, flow-through titanium footpegs, rear brake clevis, banjo bolts, top and bottom triple clamp, 1-1/8-inch oversize bar mounts and a graphics kit (with seat cover).  

Pro Circuit has a solid group of aftermarket companies that sponsor their Monster Energy/Pro Circuit race team. Mitch and the boys try to help those who help them, so they use their products whenever possible. This trickle-down effect reached our special YZ450F test bike. Renthal supplied durable TwinWall handlebars and sprockets, and RK added a gold chain for good measure.

By lengthening the link arm, the weight distribution was moved rearward, thus improving the turning characteristics.  


Engine: Although the MXA wrecking crew likes to be spoiled by testing ultra-expensive motocross bikes that should be accompanied by a security guard, we were relieved to ride Pro Circuit’s YZ450F because the engine wasn’t completely decked out. Why? MXA test riders know that Mitch Payton can craft a 60-horsepower 450 engine (we know because we’ve tested several), but it wasn’t power that we were after. We were looking for a better-handling bike. Okay, we admit that we did yearn for improved power out of the YZ450F engine, but we felt that we could get that with the Pro Circuit exhaust system (and some judicious tuning with the GYTR Power Tuner).

Thanks to new technology, the YZ450F feels as light as a feather in the air. Pro Circuit made the bike feel even better.

In stock form, the 2010 Yamaha YZ450F’s forks are soft. Even more disconcerting is that the front end has a busy feel with a touch of oversteer. Through Supercross testing, Bones Bacon heard the same complaints from a myriad of AMA Pro riders. He came up with a three-point plan:

(1) First, Bones went stiffer on compression in the forks and the shock and softer on the rebound. His goal was to keep the forks up in their stroke, which in turn would make them slightly more plush.

The second objective was to keep a load on the shock, letting it settle into its stroke to erase the bike’s stinkbug stance.

Finally, he changed the shock linkage to lower the chassis, firm up the shock’s damping curve, calm the bike down and allow for a wider range of fork height and race sag options. This is a great idea and vastly improved the ergos, handling and feel of the YZ450F. Best of all, it stopped the wiggle on the entrance to corners (when combined with adjustment to sag and fork height).

We made Bones move in with us and go to every test session. We wanted to have a professional at our beck-and-call so that we could iron out any quibbles. For his part, Bones wanted to be there because he learns something new every time he tests. In the end, we were glad that he was there when troubles arose.

We would give the stock Kayaba SSS suspension a very good grade. It’s among the best production suspension systems offered in 2010, but Pro Circuit’s tuned suspension shouldn’t even be mentioned in the same sentence. It took us a few adjustments (actually revalves) to dial in the Pro Circuit mods, but afterward the YZ450F felt like a completely different bike. All of the little quirks of the stock stuff were gone. Thanks to dialed-in suspension, the effects of the tilted cylinder and offset crank were immediately noticed. Just remember that when getting your 2010 YZ450F suspension worked on by Pro Circuit, request MXA‘s settings (otherwise you might end up with a stiffer AMA Pro setup). You won’t be disappointed.

Aside from the massaged suspension, the most noticeable modification on our Pro Circuit YZ450F was the Ti-4R exhaust system. Due to the YZ450F’s unusual tornado-style midpipe, Pro Circuit burned the midnight oil trying to perfect the length and shape of their exhaust system. The bike’s personality changed dramatically with the Ti-4R exhaust system bolted on. Faster test riders enjoyed the performance gains from mid and up. Pro Circuit equipped our test bike with a 48-tooth Renthal rear sprocket (which is the stock gearing), but we geared it down by one tooth (49). Adding an extra tooth helped slower riders get the engine up to speed quicker and jumped the YZ450F’s second-to-third gap. And faster riders were able to get to third gear sooner, which magnified their speed advantage over mere mortals.


Our Pro Circuit Yamaha YZ450F test bike was a success for several reasons:

(1) It proved that you don’t have to blow your child’s college tuition money to vastly improve the 2010 YZ450F.

We learned the intricacies of the Kayaba SSS suspension and what needed to be done in order to maximize its performance.

It was a blast to ride and race the bike.

The Yamaha is a uniquely different looking machine
and it doesn’t respond to just any hop-up mod.

Even if you don’t have your suspension worked on (and for a large number of people, the stock SSS suspension is more than adequate), consider getting the longer Pro Circuit shock linkage. This is the same trick that everyone from the factory team to privateers used on the 2009 CRF450 to stop it from stink bugging.

The Pro Circuit YZ450F cornered like a dream, handled a wide array of terrain features with ease, felt balanced and pulled hard in the midrange and top-end.

Bones Bacon found the recipe for suspension success?stiffer fork springs, different valving, and lower oil height.

As for the budget conscious, here are a few tips:

Pipe. The Yamaha YZ450F really needs an aftermarket exhaust pipe. In stock trim it had great low-to-mid power but virtually no top-end (although it will rev to the rev limiter). Aftermarket pipes broaden out the low-end and allow the engine to pull across the middle.

Linkage. Even if you don’t have your suspension worked on (and for a large number of people, the stock SSS suspension is more than adequate), consider getting the longer Pro Circuit shock linkage. This is the same trick that everyone from the factory team to privateers used on the 2009 CRF450 to stop it from stink bugging. Although it might seem that the linkage is a suspension mod, it is really more of a handling fix. It brings the rear of the chassis down, which levels the bike out, balances the front and rear, takes some of the load off the front forks and allows the frame geometry to be changed across a wider range of angles. Good stuff.

Gearing. If you can only afford one mod, gear the 2010 YZ450F down by adding one tooth to the rear (some Pro test riders went two teeth). MXA test riders varied between 49- and 50-teeth on the rear. It makes a major difference to the power delivery, but most of all it enhances the gear ratios by making third gear more usable.

For more information, visit www.procircuit.com or call (951) 738-8050.


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